The present invention relates generally to inkjet printers, and more particularly to an inkjet printing system including a spring pad which ensures electrical interconnection between electrical contacts of a printer carriage and corresponding electrical contacts of a print cartridge installed in the printer carriage.
A conventional inkjet printing system includes a printhead assembly, an ink supply which supplies liquid ink to the printhead assembly, and an electronic controller which controls the printhead assembly. The printhead assembly, commonly referred to as a print cartridge or pen, ejects ink drops through a plurality of orifices or nozzles and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead assembly and the print medium are moved relative to each other.
To position the printhead assembly relative to the print medium, the conventional inkjet print system includes a carriage assembly. As such, the printhead assembly is positioned in and supported by the carriage assembly. Typically, electrical signals which control and/or monitor operation of the printhead assembly are communicated between the electronic controller and the printhead assembly via the carriage assembly.
To communicate electrical signals between the electronic controller and the printhead assembly via the carriage assembly, the printhead assembly and the carriage assembly each include a plurality of electrical contacts. As such, the electrical contacts contact each other and establish an electrical interconnection between the printhead assembly and the carriage assembly when the printhead assembly is positioned in the carriage assembly. Understandably, the electrical contacts of the carriage assembly are electrically coupled to the electronic controller such that electrical signals are communicated between the electronic controller and the printhead assembly via the carriage assembly.
In one arrangement, the electrical contacts of the carriage assembly are part of a flexible electrical circuit which includes conductive traces formed in a flexible base material. As such, the flexible electrical circuit can flex to accommodate positional variations of the electrical contacts of the printhead assembly and/or the electrical contacts of the carriage assembly. Such variations may be caused, for example, by manufacturing tolerances of the printhead assembly and/or carriage assembly. Thus, to ensure electrical contact between the electrical contacts of the printhead assembly and the electrical contacts of the carriage assembly, compensators including elastomeric or spring pads have been associated with the flexible electrical circuit to bias the flexible electrical circuit and compensate for positional variations.
With existing elastomeric or spring pads, however, a force created between the electrical contacts of the printhead assembly and the electrical contacts of the carriage assembly typically increases as the elastomeric or spring pad is compressed. Thus, existing elastomeric or spring pads may develop excessive forces at maximum displacement. Such excessive forces may result in improper fit of the printhead assembly and the carriage assembly as well as damage to the carriage assembly and/or printhead assembly if the forces exceed the allowable design loads. To accommodate the high clamping forces required with existing spring pads, the carriage assembly must be made stiffer and the clamping system must be made stronger thus increasing the cost and size of the system.
Accordingly, a need exist for improving electrical contact between the electrical contacts of a print cartridge and the corresponding electrical contacts of a printer carriage in which the print cartridge is to be installed. In particular, a need exists for a spring pad which minimizes a maximum force developed between the electrical contacts of the print cartridge and the electrical contacts of the printer carriage when the print cartridge is installed in the printer carriage.
One aspect of the present invention provides a spring pad. The spring pad includes a base having a first side and a second side opposite the first side, and a plurality of resilient bumps protruding from the first side of the base. Each of the resilient bumps have a substantially semi-ellipsoidal shape and include a hollow interior communicating with the second side of the base.
Another aspect of the present invention provides a carriage assembly adapted to hold a printhead assembly of an inkjet printing system. The carriage assembly includes a carriage adapted to support the printhead assembly, a plurality of electrical contacts provided along a sidewall of the carriage, and a spring pad interposed between the sidewall of the carriage and the plurality of electrical contacts. As such, the spring pad includes a plurality of resilient bumps each adapted to bias a respective one of the electrical contacts away from the sidewall of the carriage. Each of the resilient bumps have a substantially semi-elliptical cross-section.
Another aspect of the present invention provides an inkjet printing system. The inkjet printing system includes a print cartridge including an inkjet printhead assembly and a first plurality of electrical contacts electrically coupled to the inkjet printhead assembly, and a printer carriage including a second plurality of electrical contacts. As such, the printer carriage is adapted to hold the print cartridge and the first plurality of electrical contacts are adapted to contact the second plurality of electrical contacts. In addition, the printer carriage includes a plurality of resilient bumps each associated with one of the second plurality of electrical contacts such that each of the resilient bumps are adapted to provide a substantially constant force between one of the first plurality of electrical contacts and one of the second plurality of electrical contacts when compressed.
Another aspect of the present invention provides a method of electrically connecting a print cartridge including an inkjet printhead assembly and a printer carriage adapted to support the print cartridge. The method includes electrically contacting at least one electrical contact of the printer carriage with at least one electrical contact of the print cartridge, and biasing the at least one electrical contact of the printer carriage against the at least one electrical contact of the print cartridge with a resilient bump associated with the at least one electrical contact of the printer carriage. Biasing the at least one electrical contact of the printer carriage against the at least one electrical contact of the print cartridge includes compressing the resilient bump and compressing the resilient bump includes buckling a sidewall of the resilient bump.